This invention is in the art of sewing machines, relates to devices for forming chain stitches in a novel and advantageous manner, involves combinations with chain stitch mechanism heretofore unattainable, and more particularly, provides for a novel arrangement which may be used in a lock stitch machine for converting the mechanism to the production of chain stitches.
Many chain stitch mechanisms and chain stitch conversion devices are known in the prior art that operate by retaining a thread loop until it has been entered by the needle on the succeeding needle penetration. All of the prior art devices further share in common the attribute that shedding of the retained thread loop is effected as the result of a movement of a part of the sewing machine mechanism which is not necessarily related to the actual seizure and manipulation of the succeeding loop of thread. As a result, if for any reason loop seizure should fail to occur, the previously formed thread loop will be released without being enchained and the resulting interruption of the chain of loops can permit the seam to be raveled.
The U.S. Pat. of Bartosz No. 3,173,390, Mar. 6, 1965, is representative of the prior art and discloses a chain stitch forming conversion device for a lock stitch sewing machine in which a web on the sewing machine feed dog, during the recurring motion of the feed dog, engages and strips the retained thread loop from a thread loop retaining finger. In the mechanism of U.S. Pat. No. 3,173,390, the thread loop will be shed from the thread retainer whether or not the loop taker beak is successful in seizing the succeeding thread loop from the needle.